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          原生 JS 封装数组方法
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        <h2 id="数组基本操作方法"><a href="#数组基本操作方法" class="headerlink" title="数组基本操作方法"></a>数组基本操作方法</h2><blockquote>
<p>以下方法<strong>均改变原数组</strong>，需要操作数组的 length 属性</p>
</blockquote>
<h3 id="Push"><a href="#Push" class="headerlink" title="Push"></a>Push</h3><ul>
<li>返回值：新数组的长度</li>
<li>思路：数组的长度等于 <code>arguments[i]</code></li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myPush = <span class="function"><span class="keyword">function</span> (<span class="params"></span>) </span>&#123;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">arguments</span>.length; i++) &#123;</span><br><span class="line">        <span class="built_in">this</span>[<span class="built_in">this</span>.length] = <span class="built_in">arguments</span>[i];</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> <span class="built_in">this</span>.length;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h3 id="Pop"><a href="#Pop" class="headerlink" title="Pop"></a>Pop</h3><ul>
<li>返回值：删除的项（如果空数组，返回 undefined）</li>
<li>思路：让数组长度 -1</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myPop = <span class="function"><span class="keyword">function</span> (<span class="params"></span>) </span>&#123;</span><br><span class="line">    <span class="keyword">return</span> <span class="built_in">this</span>.length==<span class="number">0</span>?<span class="literal">undefined</span>:(<span class="built_in">this</span>[<span class="built_in">this</span>.length - <span class="number">1</span>],<span class="built_in">this</span>.length--);</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h3 id="Shift"><a href="#Shift" class="headerlink" title="Shift"></a>Shift</h3><ul>
<li>返回值：删除的项</li>
<li>思路：让数组前一个值 <code>this[i]</code> 等于后一个值 <code>this[i + 1]</code> ，之后把数组长度 -1</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myShift = <span class="function"><span class="keyword">function</span> (<span class="params"></span>) </span>&#123;</span><br><span class="line">    <span class="keyword">if</span> (<span class="built_in">this</span>.length == <span class="number">0</span>) &#123;</span><br><span class="line">        <span class="keyword">return</span>;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">let</span> del = <span class="built_in">this</span>[<span class="number">0</span>];</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">this</span>.length; i++) &#123;</span><br><span class="line">        <span class="built_in">this</span>[i] = <span class="built_in">this</span>[i + <span class="number">1</span>];</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="built_in">this</span>.length--;</span><br><span class="line">    <span class="keyword">return</span> del;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h3 id="Unshift"><a href="#Unshift" class="headerlink" title="Unshift"></a>Unshift</h3><ul>
<li>返回值：新数组的长度</li>
<li>思路：让数组后一个值 <code>this[i]</code> 等于前 n（<code>n=arguments.length</code>）个值 <code>this[i - arguments.length]</code> ，之后把前 n 个值填为 <code>arguments[i]</code></li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myUnshift = <span class="function"><span class="keyword">function</span> (<span class="params"></span>) </span>&#123;</span><br><span class="line">    <span class="built_in">this</span>.length += <span class="built_in">arguments</span>.length;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="built_in">this</span>.length - <span class="number">1</span>; i &gt;= <span class="number">0</span>; i--) &#123;</span><br><span class="line">        <span class="keyword">if</span> (i &gt;= <span class="built_in">arguments</span>.length) &#123;</span><br><span class="line">            <span class="built_in">this</span>[i] = <span class="built_in">this</span>[i - <span class="built_in">arguments</span>.length];</span><br><span class="line">        &#125; <span class="keyword">else</span> &#123;</span><br><span class="line">            <span class="built_in">this</span>[i] = <span class="built_in">arguments</span>[i];</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> <span class="built_in">this</span>.length;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<ul>
<li>ES6 方法实现能简单一些。其实就是拼接数组，之后把拼接的数组一项一项赋值给原数组</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myUnshift = <span class="function"><span class="keyword">function</span> (<span class="params">...arg</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">var</span> newArr = [...arg, ...this];</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; newArr.length; i++) &#123;</span><br><span class="line">        <span class="built_in">this</span>[i] = newArr[i];</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> <span class="built_in">this</span>.length;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h2 id="数组操作方法"><a href="#数组操作方法" class="headerlink" title="数组操作方法"></a>数组操作方法</h2><blockquote>
<p>以下方法除splice（改变原数组）<strong>均不改变原数组</strong></p>
</blockquote>
<h3 id="splice（特殊）"><a href="#splice（特殊）" class="headerlink" title="splice（特殊）"></a>splice（特殊）</h3><blockquote>
<p>因为 push 实现比较简单，这里用到了 push 方法，能简写一两行</p>
</blockquote>
<ul>
<li><p>返回值：删除的项（数组）</p>
</li>
<li><p>思路：按参数数量分别进行判定</p>
<ul>
<li>参数小于等于1个，从 start 开始添加到新数组，并把添加那项删除（数组长度也减少）</li>
<li>参数大于1个，先进行删除（跟上一步相同）再把数组分成三份，左边+中间被替换的项+右边，合并数组</li>
</ul>
<p>注意：</p>
<ol>
<li>第一个参数为负数：如果转换为正数，大于数组长度，直接转换为0；小于等于数组长度，需加上数组长度</li>
<li>第二个参数：如果小于0，直接转换为0</li>
<li>第三个参数起：要添加的项</li>
</ol>
</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.mySplice = <span class="function"><span class="keyword">function</span> (<span class="params">start, del</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">let</span> arr = [];</span><br><span class="line">    <span class="keyword">if</span> (start &lt; <span class="number">0</span>) &#123;</span><br><span class="line">        start = -start &gt; <span class="built_in">this</span>.length ? <span class="number">0</span> : <span class="built_in">this</span>.length + start;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">if</span> (<span class="built_in">arguments</span>.length &lt;= <span class="number">1</span>) &#123;</span><br><span class="line">        <span class="keyword">for</span> (<span class="keyword">let</span> i = start; i &lt; <span class="built_in">this</span>.length; i++) &#123;</span><br><span class="line">            arr.push(<span class="built_in">this</span>[i]);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="built_in">this</span>.length = start;</span><br><span class="line">    &#125; <span class="keyword">else</span> &#123;</span><br><span class="line">        del = del &lt; <span class="number">0</span> ? <span class="number">0</span> : del;</span><br><span class="line">        <span class="comment">// 删除数组这一步</span></span><br><span class="line">        <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; del; i++) &#123;</span><br><span class="line">            arr.push(<span class="built_in">this</span>[start + i]);</span><br><span class="line">            <span class="built_in">this</span>[start + i] = <span class="built_in">this</span>[start + i + del];</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="built_in">this</span>.length -= del;</span><br><span class="line">        <span class="keyword">let</span> lArr = [];</span><br><span class="line">        <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; start; i++) &#123;</span><br><span class="line">            lArr.push(<span class="built_in">this</span>[i]);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">arguments</span>.length - <span class="number">2</span>; i++) &#123;</span><br><span class="line">            lArr.push(<span class="built_in">arguments</span>[i + <span class="number">2</span>]);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">for</span> (<span class="keyword">let</span> i = start; i &lt; <span class="built_in">this</span>.length; i++) &#123;</span><br><span class="line">            lArr.push(<span class="built_in">this</span>[i]);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; lArr.length; i++) &#123;</span><br><span class="line">            <span class="built_in">this</span>[i] = lArr[i];</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> arr;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<ul>
<li>删除数组那一步，我第一时间想到的是冒泡（把删除项一次一次冒到最后一位），最后出来的代码是下面这样（非常麻烦）</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> that = del;</span><br><span class="line"><span class="keyword">for</span> (<span class="keyword">let</span> i = that; i &gt; <span class="number">0</span>; i++) &#123;</span><br><span class="line">    <span class="keyword">if</span> (that &lt;= <span class="number">0</span>) &#123;</span><br><span class="line">        <span class="keyword">break</span>;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> j = start; j &lt; <span class="built_in">this</span>.length - <span class="number">1</span>; j++) &#123;</span><br><span class="line">        [<span class="built_in">this</span>[j], <span class="built_in">this</span>[j + <span class="number">1</span>]] = [<span class="built_in">this</span>[j + <span class="number">1</span>], <span class="built_in">this</span>[j]];</span><br><span class="line">    &#125;</span><br><span class="line">    arr.push(<span class="built_in">this</span>[<span class="built_in">this</span>.length - <span class="number">1</span>]);</span><br><span class="line">    <span class="built_in">this</span>.length--;</span><br><span class="line">    that--;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<ul>
<li>大可不必这样，把删除项的下一位（不删除）往前挪一个一个覆盖要删除的项即可</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; del; i++) &#123;</span><br><span class="line">    arr.push(<span class="built_in">this</span>[start + i]);</span><br><span class="line">    <span class="built_in">this</span>[start + i] = <span class="built_in">this</span>[start + i + del];</span><br><span class="line">&#125;</span><br><span class="line"><span class="built_in">this</span>.length -= del;</span><br></pre></td></tr></table></figure>

<h3 id="concat"><a href="#concat" class="headerlink" title="concat"></a>concat</h3><ul>
<li>返回值：拼接后的新数组</li>
<li>思路：如果参数是数组需遍历后一个一个添加到新数组</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myConcat = <span class="function"><span class="keyword">function</span> (<span class="params"></span>) </span>&#123;</span><br><span class="line">    <span class="keyword">let</span> arr = [];</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">this</span>.length; i++) &#123;</span><br><span class="line">        arr[i] = <span class="built_in">this</span>[i];</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">arguments</span>.length; i++) &#123;</span><br><span class="line">        <span class="keyword">const</span> el = <span class="built_in">arguments</span>[i];</span><br><span class="line">        <span class="keyword">if</span> (<span class="built_in">Array</span>.isArray(el)) &#123;</span><br><span class="line">            <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; el.length; i++) &#123;</span><br><span class="line">                arr[arr.length] = el[i];</span><br><span class="line">            &#125;</span><br><span class="line">        &#125; <span class="keyword">else</span> &#123;</span><br><span class="line">            arr[arr.length] = el;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> arr;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h3 id="slice"><a href="#slice" class="headerlink" title="slice"></a>slice</h3><ul>
<li>返回值：复制后的新数组</li>
<li>思路：如果传参是负数索引，需对其长度进行判定。如果大于数组长度，将其改为0；小于数组长度，将其改为<code>arr.length+(负数索引)</code></li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.mySlice = <span class="function"><span class="keyword">function</span> (<span class="params">start = <span class="number">0</span>, end = <span class="built_in">this</span>.length</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">var</span> arr = [];</span><br><span class="line">    <span class="keyword">if</span> (start &lt; <span class="number">0</span>) &#123;</span><br><span class="line">        start = -start &gt; <span class="built_in">this</span>.length ? <span class="number">0</span> : <span class="built_in">this</span>.length + start;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">if</span> (end &lt; <span class="number">0</span>) &#123;</span><br><span class="line">        end = -end &gt; <span class="built_in">this</span>.length ? <span class="number">0</span> : <span class="built_in">this</span>.length + end;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = start; i &lt; end; i++) &#123;</span><br><span class="line">        arr.push(<span class="built_in">this</span>[i]);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> arr;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h3 id="flat"><a href="#flat" class="headerlink" title="flat"></a>flat</h3><ul>
<li>返回值：扁平后的新数组</li>
<li>思路：递归（下面实现没有加上可以指定递归深度的参数，类似<code>arr.flat(Infinity)</code>）</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myFlat = <span class="function"><span class="keyword">function</span> (<span class="params"></span>) </span>&#123;</span><br><span class="line">    <span class="keyword">let</span> arr = [];</span><br><span class="line">    fn(<span class="built_in">this</span>);</span><br><span class="line">    <span class="function"><span class="keyword">function</span> <span class="title">fn</span>(<span class="params">ary</span>) </span>&#123;</span><br><span class="line">        <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; ary.length; i++) &#123;</span><br><span class="line">            <span class="keyword">const</span> item = ary[i];</span><br><span class="line">            <span class="keyword">if</span> (<span class="built_in">Array</span>.isArray(item)) &#123;</span><br><span class="line">                fn(item);</span><br><span class="line">            &#125; <span class="keyword">else</span> &#123;</span><br><span class="line">                arr.push(item);</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> arr;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br><span class="line"><span class="built_in">Array</span>.prototype.myFlat = <span class="function"><span class="keyword">function</span> (<span class="params"></span>) </span>&#123;</span><br><span class="line">    <span class="keyword">return</span> <span class="built_in">this</span>.toString().split(<span class="string">&quot;,&quot;</span>).map(<span class="function">(<span class="params">item</span>) =&gt;</span> <span class="built_in">Number</span>(item));</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>



<h2 id="数组重排方法"><a href="#数组重排方法" class="headerlink" title="数组重排方法"></a>数组重排方法</h2><h3 id="reverse"><a href="#reverse" class="headerlink" title="reverse"></a>reverse</h3><ul>
<li>返回值：倒序后的数组</li>
<li>思路：第n个数和倒数第n个数两两对换</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myReverse = <span class="function"><span class="keyword">function</span> (<span class="params"></span>) </span>&#123;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>, j = <span class="built_in">this</span>.length - <span class="number">1</span>; j &gt; i; i++, j--) &#123;</span><br><span class="line">        <span class="keyword">var</span> temp = <span class="built_in">this</span>[i];</span><br><span class="line">        <span class="built_in">this</span>[i] = <span class="built_in">this</span>[j];</span><br><span class="line">        <span class="built_in">this</span>[j] = temp;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> <span class="built_in">this</span>;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h3 id="sort"><a href="#sort" class="headerlink" title="sort"></a>sort</h3><ul>
<li>返回值：排序后的数组</li>
<li>思路：不传参的时候，两两比较 String(xxx) 的值；传参的时候判断 <code>callBack(a-b)</code> 是否大于 0 即可</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.mySort = <span class="function"><span class="keyword">function</span> (<span class="params">callBack</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">if</span> (<span class="built_in">this</span>.length &lt;= <span class="number">1</span>) &#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="built_in">this</span>;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">if</span> (<span class="keyword">typeof</span> callBack === <span class="string">&quot;function&quot;</span>) &#123;</span><br><span class="line">        <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">this</span>.length - <span class="number">1</span>; i++) &#123;</span><br><span class="line">            <span class="keyword">for</span> (<span class="keyword">let</span> j = <span class="number">0</span>; j &lt; <span class="built_in">this</span>.length - <span class="number">1</span> - i; j++) &#123;</span><br><span class="line">                <span class="keyword">if</span> (callBack(<span class="built_in">this</span>[j], <span class="built_in">this</span>[j + <span class="number">1</span>]) &gt; <span class="number">0</span>) &#123;</span><br><span class="line">                    [<span class="built_in">this</span>[j], <span class="built_in">this</span>[j + <span class="number">1</span>]] = [<span class="built_in">this</span>[j + <span class="number">1</span>], <span class="built_in">this</span>[j]];</span><br><span class="line">                &#125;</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125; <span class="keyword">else</span> <span class="keyword">if</span> (<span class="keyword">typeof</span> callBack === <span class="string">&quot;undefined&quot;</span>) &#123;</span><br><span class="line">        <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">this</span>.length - <span class="number">1</span>; i++) &#123;</span><br><span class="line">            <span class="keyword">for</span> (<span class="keyword">let</span> j = <span class="number">0</span>; j &lt; <span class="built_in">this</span>.length - <span class="number">1</span> - i; j++) &#123;</span><br><span class="line">                <span class="keyword">if</span> (<span class="built_in">String</span>(<span class="built_in">this</span>[j]) &gt; <span class="built_in">String</span>(<span class="built_in">this</span>[j + <span class="number">1</span>])) &#123;</span><br><span class="line">                    [<span class="built_in">this</span>[j], <span class="built_in">this</span>[j + <span class="number">1</span>]] = [<span class="built_in">this</span>[j + <span class="number">1</span>], <span class="built_in">this</span>[j]];</span><br><span class="line">                &#125;</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125; <span class="keyword">else</span> &#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="string">&quot;参数异常&quot;</span>;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> <span class="built_in">this</span>;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h2 id="数组位置方法"><a href="#数组位置方法" class="headerlink" title="数组位置方法"></a>数组位置方法</h2><blockquote>
<p>以下方法均<strong>不改变原数组</strong></p>
</blockquote>
<h3 id="indexOf"><a href="#indexOf" class="headerlink" title="indexOf"></a>indexOf</h3><ul>
<li>返回值：索引/-1</li>
<li>思路：遍历数组，第二个参数是从哪个索引开始。如果不传参，从头查到尾部</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myIndexOf = <span class="function"><span class="keyword">function</span> (<span class="params">val, index = <span class="number">0</span></span>) </span>&#123;</span><br><span class="line">    <span class="keyword">if</span> (index &lt; <span class="number">0</span>) &#123;</span><br><span class="line">        index = -index &gt; <span class="built_in">this</span>.length ? <span class="number">0</span> : index + <span class="built_in">this</span>.length;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = index; i &lt; <span class="built_in">this</span>.length; i++) &#123;</span><br><span class="line">        <span class="keyword">if</span> (<span class="built_in">this</span>[i] === val) &#123;</span><br><span class="line">            <span class="keyword">return</span> i;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> -<span class="number">1</span>;</span><br><span class="line">&#125;;</span><br><span class="line"></span><br></pre></td></tr></table></figure>

<h3 id="lastIndexOf"><a href="#lastIndexOf" class="headerlink" title="lastIndexOf"></a>lastIndexOf</h3><ul>
<li>返回值：索引/-1</li>
<li>思路：遍历数组，第二个参数是到哪个索引结束（从0开始到这个索引结束）。如果不传参，从头查到尾部</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myLastIndexOf = <span class="function"><span class="keyword">function</span> (<span class="params">val, index = <span class="built_in">this</span>.length</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">if</span> (index &lt; <span class="number">0</span>) &#123;</span><br><span class="line">        index = -index &gt;= <span class="built_in">this</span>.length ? <span class="number">0</span> : index + <span class="built_in">this</span>.length;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = index; i &gt;= <span class="number">0</span>; i--) &#123;</span><br><span class="line">        <span class="keyword">if</span> (<span class="built_in">this</span>[i] === val) &#123;</span><br><span class="line">            <span class="keyword">return</span> i;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> -<span class="number">1</span>;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h3 id="includes"><a href="#includes" class="headerlink" title="includes"></a>includes</h3><ul>
<li>返回值：true/false</li>
<li>思路：遍历数组</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myIncludes = <span class="function"><span class="keyword">function</span> (<span class="params">val</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">this</span>.length; i++) &#123;</span><br><span class="line">        <span class="keyword">if</span> (<span class="built_in">this</span>[i] === val) &#123;</span><br><span class="line">            <span class="keyword">return</span> <span class="literal">true</span>;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> <span class="literal">false</span>;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h2 id="数组迭代方法"><a href="#数组迭代方法" class="headerlink" title="数组迭代方法"></a>数组迭代方法</h2><blockquote>
<p>以下方法均<strong>不改变原数组</strong></p>
</blockquote>
<h3 id="forEach"><a href="#forEach" class="headerlink" title="forEach"></a>forEach</h3><blockquote>
<p>回调函数内部 this 一般指向 window</p>
</blockquote>
<ul>
<li>返回值：undefined</li>
<li>思路：遍历数组</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myForEach = <span class="function"><span class="keyword">function</span> (<span class="params">callBack</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">this</span>.length; i++) &#123;</span><br><span class="line">        <span class="keyword">let</span> index = i, item = <span class="built_in">this</span>[i];</span><br><span class="line">        callBack(item, index);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h3 id="map"><a href="#map" class="headerlink" title="map"></a>map</h3><ul>
<li>返回值：映射后的新数组</li>
<li>思路：遍历数组，把数组每以项经过运算后赋值给新数组</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myMap = <span class="function"><span class="keyword">function</span> (<span class="params">callBack</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">let</span> arr = [];</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">this</span>.length; i++) &#123;</span><br><span class="line">        <span class="keyword">let</span> index = i, item = <span class="built_in">this</span>[i];</span><br><span class="line">        arr[i] = callBack(item, index);</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> arr;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h3 id="reduce"><a href="#reduce" class="headerlink" title="reduce"></a>reduce</h3><ul>
<li>返回值：函数累计处理的结果</li>
<li>思路：initial 返回值在数组的每次迭代中被记住，最后成为最终的结果值</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myReduce = <span class="function"><span class="keyword">function</span> (<span class="params">callBack, initial</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">if</span> (<span class="keyword">typeof</span> callBack !== <span class="string">&quot;function&quot;</span>) <span class="keyword">throw</span> <span class="keyword">new</span> <span class="built_in">TypeError</span>(<span class="string">&quot;callBack must be function&quot;</span>);</span><br><span class="line">    <span class="keyword">let</span> i = <span class="number">0</span>;</span><br><span class="line">    <span class="keyword">if</span> (<span class="keyword">typeof</span> initial === <span class="string">&quot;undefined&quot;</span>) &#123;</span><br><span class="line">        initial = <span class="built_in">this</span>[<span class="number">0</span>];</span><br><span class="line">        i = <span class="number">1</span>;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">for</span> (; i &lt; <span class="built_in">this</span>.length; i++) &#123;</span><br><span class="line">        initial = callBack(initial, <span class="built_in">this</span>[i], i)</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> initial;</span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h3 id="find"><a href="#find" class="headerlink" title="find"></a>find</h3><ul>
<li>返回值：找到就返回符合的元素，没有返回 undefined</li>
<li>思路：遍历数组</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myFind = <span class="function"><span class="keyword">function</span> (<span class="params">callBack</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">this</span>.length; i++) &#123;</span><br><span class="line">        <span class="keyword">if</span> (callBack(<span class="built_in">this</span>[i], i)) <span class="keyword">return</span> <span class="built_in">this</span>[i]</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h3 id="every"><a href="#every" class="headerlink" title="every"></a>every</h3><ul>
<li>返回值：只要有一个不符合返回false，如果都符合返回 true</li>
<li>思路：遍历数组，一假即假</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myEvery = <span class="function"><span class="keyword">function</span> (<span class="params">callBack</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">this</span>.length; i++) &#123;</span><br><span class="line">        <span class="keyword">if</span> (!callBack(<span class="built_in">this</span>[i], i)) <span class="keyword">return</span> <span class="literal">false</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> <span class="literal">true</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h3 id="some"><a href="#some" class="headerlink" title="some"></a>some</h3><ul>
<li>返回值：只要有一个符合就返回 true，如果都符合返回 false</li>
<li>思路：遍历数组，一真即真</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.mySome = <span class="function"><span class="keyword">function</span> (<span class="params">callBack</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">this</span>.length; i++) &#123;</span><br><span class="line">        <span class="keyword">if</span> (callBack(<span class="built_in">this</span>[i], i)) <span class="keyword">return</span> <span class="literal">true</span></span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> <span class="literal">false</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h3 id="filter"><a href="#filter" class="headerlink" title="filter"></a>filter</h3><ul>
<li>返回值：一个新数组，数组里面是符合条件的所有元素</li>
<li>思路：遍历数组</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">Array</span>.prototype.myFilter = <span class="function"><span class="keyword">function</span> (<span class="params">callBack</span>) </span>&#123;</span><br><span class="line">    <span class="keyword">if</span> (!<span class="built_in">Array</span>.isArray(<span class="built_in">this</span>) || !<span class="built_in">this</span>.length || <span class="keyword">typeof</span> callback !== <span class="string">&#x27;function&#x27;</span>) &#123;</span><br><span class="line">        <span class="keyword">return</span> []</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">let</span> arr = [];</span><br><span class="line">    <span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; <span class="built_in">this</span>.length; i++) &#123;</span><br><span class="line">        <span class="keyword">if</span> (!callBack(<span class="built_in">this</span>[i], i)) &#123;</span><br><span class="line">            arr.push(<span class="built_in">this</span>[i]);</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="keyword">return</span> arr</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>


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